1. Field of the Invention
The present invention relates generally to motor control systems and, more particularly, to a multiple pulse width modulation digital motor control system to control both the motor speed and direction of rotation for D.C. or A.C. electric motors.
2. Description of the Background
Prior art motor control systems generally operate with significant inefficiencies such as high heat dissipation, and/or have problems related to changing the motor rotation direction. The circuitry shown in my previous U.S. Pat. No. 7,421,193, which is incorporated in its entirety herein by reference, discloses a motor control with very low heat dissipation, which in one embodiment provides a controller for speed and motor direction. However, a disadvantage of the circuitry taught in my previous patent is that the maximum forward and reverse pulse had only a 50% duty cycle.
For a servo power control system to operate reliably without failure, the system design should always consider the power dissipation and the flexibility of the design in allowing its application to large and small motors. This may be especially important in applications where the available power may be limited.
Open loop motor speed control systems have used variations of the time durations of pulses applied to the motor due to their efficient use of power, which especially useful for battery operated devices. An example is in application to a variable speed drill, screwdriver, or socket driver wherein a mechanical switch is used to control motor direction. The inconvenience in having to mechanically change motor direction has been accepted as a necessity, although it would be desirable for some workers who have only one hand for operation to be able to change motor direction without manually operating a switch.
The following patents represent background art in motor controls of various types and show prior art attempts to solve the above and/or related problems as discussed above:
U.S. Pat. No. 3,206,665, issued Sep. 14, 1965, to C. Burlingham, discloses a digital motor control servo system having a source of command pulses indicative of a desired motor speed, a source of feedback pulses indicative of actual motor speed, a reversible binary counter connected to those sources so as to accumulate the difference between the total number of pulses delivered by each source, control means for varying the motor speed in accordance with the accumulated count, and inhibition means connected between the sources and the counter to the output of the counter to prevent pulses from reaching the counter whenever the pulses would oversaturate the counter.
U.S. Pat. No. 3,612,974, issued Oct. 12, 1971, to Wolf et al., discloses a motor that generates first pulses having a frequency related to the speed of rotation of the motor, second pulses generated in response to the first pulses having durations at least greater than a minimum time duration, and third pulses generated and used to pulse drive the motor having durations related to the time differences between the terminations of the second pulses and the initiations of the first pulses.
U.S. Pat. No. 3,766,459, issued Oct. 16, 1973, to McIntosh et al., discloses a control system for a machine tool having a direct current motor capable of rotating the motor shaft in a series of discrete steps through a range and maintaining the shaft in position between the steps. The motor is controlled by a digital to analog converter which receives an input having a bi-directional digital counter. A pulse generator inputs a preselected number of pulses in a preselected direction. An encoder responsive to the angular position of the motor shaft produces a fixed number of pulses for a given rotation, and the pulses count the counter in a direction related to the direction of movement of the motor shaft. Circuitry is provided both to match a directional signal with each pulse to control the counter direction and also for buffering all of the pulses to prevent more than one pulse from reaching the bi-directional digital counter at substantially the same time.
U.S. Pat. No. 3,858,100, issued Dec. 31, 1974, to Bussi et al., discloses a digital phase control adjustment system for a D.C. motor which finds particular utility in applications where fast start and stop operations of the motor are required. The pulses forming a reference signal and those forming a variable signal are stored sequentially in a shift register and when the shift register is alternately storing ones and zeros, the pulses of the two signals are in alternate sequence for a certain number of periods, indicating that the motor speed is near the intended value.
U.S. Pat. No. 3,898,545, issued Aug. 5, 1975, to Coppa et al., discloses a motor control circuit for maintaining a d-c electric motor at a constant speed, including a speed sensing means connected to the d-c electric motor to generate motor pulses whose duration is inversely proportional to the speed of the d-c electric motor, a bistable means for providing a continuous drive signal to the d-c electric motor and responsive to the application of the motor pulses and to the application of reference pulses generated by the motor pulses. The bistable means drives the d-c electric motor as long as the fixed duration of the reference pulses is shorter than the duration of the motor pulses being generated due to the rotation of the armature of the electric motor. Delay means are provided in the circuit to prevent ambiguity at the bistable means due to the simultaneous application of both the motor pulses and reference pulses to the bistable means.
U.S. Pat. No. 3,942,084, issued Mar. 2, 1976, to Louth, discloses a motor drive and servo systems particularly useful in high quality broadcast video tape recorders. A sine/cosine drive for a brushless DC motor permits high motor efficiency in a system adapted for use in a servo loop. A technique for phase locking a pair of frequency related phase locked control variable signals to a pair of frequency related reference signals, horizontal and vertical sync signals, for example, provides the advantages and precision of closed loop correction at widely variable correction rates. More accurate tape shuttling in a VTR is provided by running a DC motor in a phase locked loop as a synchronous motor and more accurate stopping of the tape is provided by comparing the capstan speed to ground in a closed loop. Improved tape tension control in the head area is provided by a pair of vacuum columns controlled by an error signal derived from the peak-to-peak tension error.
U.S. Pat. No. 4,008,424, issued Feb. 15, 1977, to G. Bompani, discloses an error voltage signal which is of magnitude related to the difference between the actual speed of a D.C. motor and a desired speed that is selectively applied to either the inverting input terminal of an operational amplifier or to its non-inverting input terminal, dependent upon the direction of rotation of the motor. The circuit components connecting the error signal to the input terminals are selected to provide the same absolute value of gain for the amplifier regardless of whether the input is to the inverting terminal or to the non-inverting terminal. The system substantially reduces complexity and diminishes the number of components required for this type of bidirectional speed regulation.
U.S. Pat. No. 4,100,012, issued Jul. 11, 1978, to Meihofer et al., discloses a web splicing apparatus that employs a pair of driven nip rolls which controllably feed web from a running roll into a festoon as web is drawn out of the festoon at a constant rate by a downstream web consuming machine. The nip rolls are driven by a DC motor connected in a closed loop servo system which compares the speed of the web entering the festoon with the web line speed to develop a command signal for the motor. During normal operation, the command signal includes a web velocity trim signal developed by monitoring the position of the festoon dancer relative to a selected reference position so as to minimize tension upsets and to maintain the dancer within its control range. During a splice sequence, the command signal comprises a deceleration ramp having a selected slope to provide controlled deceleration of the web to minimize tension upsets and to permit actuation of the splicing nips prior to actual web stop. After the splice is made, the command signal comprises an acceleration ramp whose slope is automatically adjusted to apply the least necessary tension to the ready web for new roll acceleration consistent with a given splicing speed. Further with this arrangement, the gain of the system is independent of the changing size of the expiring roll.
U.S. Pat. No. 4,100,012, issued Jul. 11, 1978, to Meihofer et al, discloses a web splicing apparatus that employs a pair of driven nip rolls which controllably feed web from a running roll into a festoon as web is drawn out of the festoon at a constant rate by a downstream web consuming machine. The nip rolls are driven by a DC motor connected in a closed loop servo system which compares the speed of the web entering the festoon with the web line speed to develop a command signal for the motor. During normal operation, the command signal includes a web velocity trim signal developed by monitoring the position of the festoon dancer relative to a selected reference position so as to minimize tension upsets and to maintain the dancer within its control range. During a splice sequence, the command signal comprises a deceleration ramp having a selected slope to provide controlled deceleration of the web to minimize tension upsets and to permit actuation of the splicing nips prior to actual web stop. After the splice is made, the command signal comprises an acceleration ramp whose slope is automatically adjusted to apply the least necessary tension to the ready web for new roll acceleration consistent with a given splicing speed. Further with this arrangement, the gain of the system is independent of the changing size of the expiring roll.
U.S. Pat. No. 4,145,644, issued Mar. 20, 1979, to R. Liu, discloses a stepping motor control circuit permitting selective operation of the motor in various modes such as half or full step mode. The circuit includes a pulse generator producing pulses at a selected motor step rate. A switch means selects the step size while a second switch selects the motor direction. An up/down counter counts pulses from the pulse generator in a direction correlated with the selected rotation direction. A read-only-memory is addressed as a function of the periodically repeating count in the up/down counter and the selected step size. The stored information at the addressed read-only-memory location actuates motor drive circuitry which generates energizing signals for the motor windings to drive the motor in the selected direction a distance corresponding to the selected step size at a step rate equal to the pulse rate of the pulse generator.
U.S. Pat. No. 4,205,260, issued May 27, 1980, to Maeda et al., discloses a motor control system including a clock pulse generator. Use is made of the clock pulses for deriving digitally, the speed-above-normal signal, the starting signal, the brake-release signal and the normal or forward rotation signal for displaying the normal or forward rotation. In response to the starting signal, 100% torque control voltage is generated and in case of the forced reversal in rotation, 100% torque control voltage for preventing the rotation in the reverse direction is generated.
U.S. Pat. No. 4,295,082, issued Oct. 13, 1981, to Moto et al., discloses a motor servo circuit. The motor in the motor servo circuit is driven by an output which is obtained by logically adding output pulses of a pulse stretcher circuit which stretches a pulse width of error pulses generated from an OR circuit when pulses inputted to the motor servo circuit and pulses outputted from a pulse generator in response to the input pulses are different in the pulse width to pulses having a predetermined pulse width which are generated at intervals of a predetermined member of the error pulses synchronizing therewith.
U.S. Pat. No. 4,409,529, issued Oct. 11, 1983, to Basford et al., discloses a prosthesis comprising: (a) a gripping member; (b) an operating lever mounted to pivot about a pivot axis and operatively connected to the gripping member; (c) a power unit including an electric motor, and a drive shaft rotatable by the electric motor; (d) means connecting the drive shaft to the operating lever at a region spaced from the pivot axis of the operating lever, the connecting means being constructed so that when the drive shaft rotates the connecting means (and also the region of the operating lever connected to the shaft) travels axially along the shaft thereby causing the operating lever to pivot about its pivot axis; and (e) means pivotally mounting the power unit to allow the connecting means to move along an arcuate path about the pivot axis during pivoting of the operating lever.
U.S. Pat. No. 4,651,269, issued Mar. 17, 1987, to K. Matsumura, discloses a circuit for reversing an electric current flow comprising a motor, a circuit formed of a first transistor at a power source side and a third transistor at the ground side which are connected in series, a circuit formed of a second transistor at the power source side and a fourth transistor at the ground side which are connected in series, the junction of the first and third transistors being connected to one terminal of the motor and the junction of the second and fourth transistors being connected to the other terminal of the motor, and a pulse generator for producing an output signal which delays the turn-on timing of the third or fourth transistor until the state of the first or second transistor has been changed from an on-state to an off-state.
U.S. Pat. No. 4,693,583, issued Sep. 15, 1987, to Ogihara et al., discloses a programmable shutter of the type wherein a shutter blade is opened and closed by means of a stepping motor. The motor is rotated in a forward direction by drive pulses of a predetermined fixed period to gradually open a sector while at the same time a light measuring circuit is started. Thus, at the time when an appropriate exposure quantity is reached, the direction of rotation of the motor is forcibly reversed to effect closing of the sector to attain simultaneous measurement of light and exposure.
U.S. Pat. No. 4,703,244, issued Oct. 27, 1987, to Takeuchi et al., discloses a frequency divided pulse produced by frequency dividing a clock signal by speed instruction data. When the current position of the pulse motor has not yet reached a set desired position, a frequency divided pulse is outputted as a forward rotation control pulse. When the current position has exceeded said set position, a frequency divided pulse is outputted as a reverse rotation control pulse. If the set desired position is changed while the pulse motor is rotating, this change of setting is detected and the output of the frequency divided pulse is inhibited for a predetermined settling period of time, thereby stopping the pulse motor. After the vibration of the rotor which occurs during the stepping of the pulse motor is settled, the reverse rotation of the pulse motor can be started, thereby preventing the occurrence of the step-out phenomenon of the pulse motor upon reverse rotation.
U.S. Pat. No. 5,334,924, issued Aug. 2, 1994, to Kawada et al, discloses that speed control of an induction motor is effected in digital fashion through use of a computer but without complex processing, and with a computer that need not be large in scale. This is accomplished by processing at least a speed command signal, actual speed signal and torque signal in analog fashion, enabling simplification of an induction motor speed control digital processing section which performs all other control operations in a digital manner. In a speed control network having a closed loop, a frequency-to-voltage converter, adder-subtractor, proportional integrator, polarity determining circuit absolute value circuit and voltage-to-frequency converter are constructed of circuitry operable on the basis of analog values, with all other circuits being constructed of circuitry operable on the basis of digital values.
U.S. Pat. No. 5,729,067, issued Mar. 17, 1998, to Janutka, discloses an improved method and servo control apparatus for controlling the motion of a linear electric motor which in turn generates motion command signals to various apparatus such as a hydraulic steering system. Preferably, the servo control apparatus includes a power supply circuit, a servo amplifier circuit, a pulse width modulation circuit, an H-bridge drive circuit and an inductive position sense circuit. The voltage at a node between coil pairs in the motor is sensed and synchronously demodulated using transmission gates to develop a DC signal representative of armature position from a center location. The signal on a current shunt resistor is synchronously demodulated by transmission gates to generate a signal, the phase of which is determined with respect to the motor drive signal. The phase signal directly indicates whether the armature is off center towards drive coil or drive coil.
U.S. Pat. No. 6,018,200, issued Jan. 25, 2000, to Anderson et al, discloses the throttle of an engine in an engine driven generator system operating subject to a wide and rapidly variable load, as in supplying current to a welder, is operated such that control signals are sent to a throttle actuator for adjusting the engine throttle position in response to load changes. The throttle actuator may be a solenoid pulling against a spring in accordance with the average current through the solenoid coil. In this embodiment, the processor causes pulse width modulated signals to be applied across the solenoid coil with throttle position changes being reflected in changes to the width of the pulses, such changes in the pulse width being delayed for at least the predetermined time since the last preceding adjustment to the throttle. Alternatively, the throttle actuator may be a stepper motor which is stepped by throttle position change signals from a processor which monitors engine speed and generator load to determine whether the throttle should be adjusted and, if so, in which direction and to what extent for optimum response.
U.S. Pat. No. 6,051,943, issued Apr. 18, 2000, to Rabin et al, discloses a motor control system employing a single Hall sensor providing a position feedback signal to a control circuit. The control circuit includes a tach counter circuit, a ramp mode circuit, an interpolation circuit, and a commutation logic circuit. Drive signals are output to the motor windings by the commutation logic circuit. The control state defining the drive signals is advanced on the basis of the estimated rotor position. The estimate of the rotor position is determined by linearly interpolating between Hall signal transitions.
U.S. Pat. No. 6,058,081, issued May 2, 2000, to Schell et al, discloses an optical drive system that includes an objective lens subassembly for directing light from a light source toward an information storage medium. An amount of the directed lighted light is returned from the storage medium. An objective lens is disposed in the objective lens subassembly. A first servomotor moves, during focus capture, the objective lens to a first position, away from the first position toward the storage medium being read while looking for a maximum Quad Sum signal, and back away from the storage medium. An electronic control circuit is connected to the first servomotor. A servo error detector is coupled to the electronic control circuit and disposed in a path of light returning from the information storage medium. The servo error detector is implemented to determine when total light returned from the information storage medium exceeds a-predetermined value, to search for a first zero crossing, corresponding to when the Quad Sum signal exceeds a predetermined amplitude, and to indicate to the electronic control circuit to direct close of focus when the Quad Sum signal exceeds the predetermined amplitude.
U.S. Pat. No. 6,064,172, issued May 16, 2000, to Kuznetsov, discloses a winding fault detection system that provides classification and identification of winding faults or winding malfunctions. The fault detection system provides signals to individual electronic switches for segmented primary windings each having an electrical phase and grouped into sub-phases which are individually switch into or out of an excitation supply or isolated through the electronic switching in response to signals from the winding fault detection system. Each primary winding forms an electrical member which includes a stator having a poly-phase winding, and there is a secondary electrical member magnetically coupled with the stator. Each primary has magnetic field sensors which detect phase angle and magnitudes of radial components of air gap flux by magnetic measurement probes between each secondary electrical member and each primary electrical member and derives an electrical signal for a component of air gap flux contributing to electromagnetic torque at each position of each stator's periphery. Additionally, the system instantaneously stores data continuously derived from the magnetic sensors and determines a hierarchy of fault detection schemes.
U.S. Pat. No. 6,069,857, issued May 30, 2000, to Schell et al, discloses an optical disc drive system that is employed in conjunction with a storage medium having a plurality of data sectors each provided with a header and a data storage area. The system includes a data detection device for retrieving stored data from the storage medium and outputting a data signal, an amplifier for providing a variable gain to the data signal and outputting an amplified data signal, a detector that is responsive to the amplified data signal for evaluating a predetermined one of the sectors to ascertain whether the storage area is blank, and an automatic gain control circuit producing a gain control output for controlling the gain of the amplifier. The control circuit has a first mode and a second mode, the first mode being active during retrieval of the header and the second mode being active during retrieval of the data storage area. The system is further provided with a sampling device for sampling the gain control output during retrieval of the stored data in a respective one of the storage areas containing previously stored data. The sampling device outputs results of the sampling, and a fixed gain control circuit is responsive to the results of the sampling for outputting a fixed gain control signal. The fixed gain control signal is applied to the amplifier during evaluation of the predetermined one of the sectors.
It would be desirable to provide a low power dissipation control system without the disadvantages of the systems discussed above. Consequently, there remains a long felt need for an improved motor speed and direction control system. Those skilled in the art have long sought and will appreciate the present invention which addresses these and other problems.